We request funding for a five year proj4ect to conduct two Internet interviews with a subset of the respondents to the Health and Retirement Study (HRS), and to set up a separate Internet panel of 1,000 non-HRS respondents, who will be interviewed via Internet twice a year for four years, plus a control group of 500 non-HRS respondents, who will e interviewed once a year by telephone for four years. The data collection and analysis will inform the HRS about the potential of Internet interviewing and may serve as a tested sample for the HRS. Our proposed study covers both methodological issues and substantive issues, foremost in economics, cognitive psychology and epidemiology. In view of the current distribution of Internet access among the population (with access dropping of among older age groups), it is anticipated that in the foreseeable future the HRS will use Internet interviewing alongside other modes. This motivates the mixed mode design of the proposed study. Specifically, we aim: 1. To provide data that will permit a comparative study of the population of Internet interviewees with the population of telephone interviewees with the goal of understanding selection bias; 2. To provide more systematic insight in the properties of Internet interviewing in comparison with other modes of collecting survey data, in particular among middle aged and elderly respondents; 3. To initiate various experiments in questionnaire and question design, exploiting the potential of Internet interviewing. Special attention will be paid to the role of cognitive functioning and the suitability of the Internet as an interviewing environment. 4. To improve the measurement of various important objective variables such as consumption or wealth; 5. To develop new measurement methods for complex possibly subjective variables such as probabilities, expectations, health histories, risk attitudes and time preferences; 6. To make the data generated by these activities available to the research community. To gear the outcomes of the research towards partial and gradual implementation of Internet interviewing in the HRS as of 2004.